Coatings and films derived from clay/wax nanocomposites

Abstract

The invention provides methods for making clay/wax nanocomposites and coatings and films of same with improved chemical resistance and gas barrier properties. The invention further provides methods for making and using emulsions of such clay/wax nanocomposites. Typically, an organophillic clay is combined with a wax or wax/polymer blend such that the cohesion energy of the clay matches that of the wax or wax/polymer blend. Suitable organophilic clays include mica and phyllosilicates that have been surface-treated with edge or edge and surface modifying agents. The resulting nanocomposites have applications as industrial coatings and in protective packaging.

1. A method of preparing a nanocomposite comprising combining a surface-treated organophilic clay and a melt comprising a wax or wax and polymer, wherein the cohesion energies of the organophilic clay and the wax or wax and polymer are sufficiently matched in both the melt and solid states to produce and maintain a homogenous dispersion of the organophilic clay in both the liquid and solid nanocomposite, and further wherein the surface-treated organophillic clay comprises an anionic edge modifying surfactant adsorbed onto an edge thereof. 
     
     
       2. The method according to  claim 1 , wherein the organophilic clay is a phyllosilicate. 
     
     
       3. The method according to  claim 1 , wherein the organophilic clay is a smectite or mica. 
     
     
       4. The method according to  claim 1 , wherein the organophilic clay is a smectite selected from the group consisting of montmorillonite, hectorite, saponite, sauconite, beidellite, nontronite, synthetic smectite, and combinations of two or more thereof. 
     
     
       5. The method according to  claim 1 , wherein the wax is selected from the group consisting of paraffin, microcystalline montan, vegetable waxes, Fisher-Tropsch, polyethylene, polypropylene, polymethylene, chemically modified waxes, polymerized alpha-olefins and combinations of two or more thereof. 
     
     
       6. The method according to  claim 5 , wherein the wax is polyethylene-block-polyethylene glycol or polyethylene monoalcohol. 
     
     
       7. The method according to  claim 1 , wherein the surface-treated clay comprises about 20 to about 75 weight percent of the nanocomposite. 
     
     
       8. The method of  claim 1 , wherein the surface-treated clay comprises about 25 to 55 weight percent of the nanocomposite. 
     
     
       9. The method of  claim 1 , wherein the surface-treated clay comprises about 45 to 55 weight percent of the nanocomposite. 
     
     
       10. The method according to  claim 1 , wherein the surface-treated clay includes a nonionic polymeric hydrotrope adsorbed onto a basal surface thereof. 
     
     
       11. The method according to  claim 10 , wherein the melt comprises from about 1 to about 99 weight percent of the nanocomposite. 
     
     
       12. The method according to  claim 11 , wherein the surface-treated clay comprises from about 1 to about 15 weight percent of the nanocompo site. 
     
     
       13. The method according to  claim 11 , wherein the surface-treated clay comprises from about 3 to about 10 weight percent of the nanocomposite. 
     
     
       14. The method according to  claim 11 , wherein the wax is selected from the group consisting of paraffin, microcystalline montan, vegetable waxes, Fisher-Tropsch waxes, polyethylene, polypropylene, polymethylene, chemically modified waxes, polymerized alpha-olefins and combinations of two or more thereof. 
     
     
       15. A method for preparing a nanocomposite coating comprising applying a nanocomposite prepared by the method of  claim 10  to a substrate to form a coating of the nanocomposite on the substrate. 
     
     
       16. The method according to  claim 10 , wherein the melt comprises a wax and polymer, and the wax/polymer ratio is from about 50 to about 0.02. 
     
     
       17. The method according to  claim 16 , wherein the polymer is selected from the group consisting of low density polyethylene, linear low density polyethylene, high density polyethylene, ethylene propylene copolymers, elastomers, and ethylene copolymers, optionally containing one or more functional groups selected from the group consisting of vinyl alcohol, vinyl acetate, acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, maleic anhydride, and succinic anhydride. 
     
     
       18. A method for preparing a nanocomposite coating comprising applying a nanocomposite prepared by the method of  claim 16  to a substrate to form a coating of the nanocomposite on the substrate. 
     
     
       19. An article comprising a substrate coated with a nanocomposite wherein the coating was prepared according to the method of  claim 18 . 
     
     
       20. The method according to  claim 1 , wherein the surface-treated clay is combined with the melt as a slurry. 
     
     
       21. The method according to  claim 1 , wherein the surface-treated clay is combined with the melt under pressure less than or greater than atmospheric pressure. 
     
     
       22. The method according to  claim 1 , further comprising incorporating one or more additives into the nanocomposite. 
     
     
       23. The method according to  claim 22 , wherein the additives are selected from the group consisting of antioxidants, anticorrosion agents, reactive scavengers, UV stabilizers, and colorants. 
     
     
       24. The method according to  claim 1 , further comprising incorporating one or more organic peroxides into the nanocomposite and reacting at a suitable temperature to effect crosslinking therein. 
     
     
       25. A method for preparing an emulsion comprising mixing a nanocomposite melt prepared according to  claim 1  and an aqueous phase with sufficient shear to produce an emulsion, wherein the aqueous phase contains at least one surfactant capable of stabilizing the nanocomposite as an emulsion. 
     
     
       26. The method according to  claim 25 , further comprising preparing the surfactant in situ by combining a strong base with a weak organic acid. 
     
     
       27. The method according to  claim 26 , wherein the base is selected from the group consisting of potassium hydroxide, ammonia and organoamines. 
     
     
       28. The method according to  claim 27 , wherein the acid is a carboxylic acid. 
     
     
       29. The method according to  claim 28 , wherein the carboxylic acid is a dicarboxylic acid. 
     
     
       30. A method for preparing a nanocomposite coating comprising applying an emulsion prepared by the method of  claim 25  to a substrate to form a coating of the nanocomposite on the substrate. 
     
     
       31. An article comprising a substrate coated with a nanocomposite, wherein the coating was prepared by the method of  claim 30 . 
     
     
       32. A method for preparing an emulsion comprising mixing a nanocomposite melt and an aqueous phase with sufficient shear to produce an emulsion, wherein the aqueous phase contains at least one surfactant capable of stabilizing the nanocomposite as an emulsion, wherein
 the nanocomposite melt is prepared by combining an organophilic clay and a melt comprising a wax or wax and polymer, wherein the cohesion energies of the organophilic clay and the wax or wax and polymer are sufficiently matched in both the melt and solid states to produce and maintain a homogenous dispersion of the organophilic clay in both the liquid and solid nanocomposite; and 
 the surfactant is prepared in situ by combining a strong base with a weak organic acid; wherein the base is selected from the group consisting of potassium hydroxide, ammonia and organoamines; and the acid is a carboxylic acid. 
 
     
     
       33. The method of  claim 32  wherein the acid is a dicarboxylic acid.